This invention relates, inter alia, to sounding an alarm when an invalid patient attempts to get up from a chair or bed. Such patients are usually held in place with a positioning belt which is generally uncomfortable and distasteful to the patient, who is usually capable of working his way out of such belts. This invention eliminates the need for a belt and returns some human dignity to the patient.
U.S. Pat. No. 943,940, issued in 1909, discloses a device to signal a ticket seller how many seats in a theatre were occupied, thus indicating the remaining number of seats that could be sold. It electrically sensed the weight of a person in a chair. Since then many variations of this concept have been devised. The apparatus of this invention is a unique, inexpensive reliable variation on this concept.
A magnetic reed switch consists of four basic parts: (1) glass capsule, (2) gas (atmosphere inside the glass capsule), (3) contacts and (4) reeds (leads). The reeds are hermetically sealed into the glass capsule in cantilever fashion so that the ends align and overlap, but with a small air gap in a normally open switch.
Because the reeds are ferromagnetic, the extreme ends will assume opposite magnetic polarity when brought into the influence of a magnetic field. When the magnetic flux density is sufficient, the attraction forces of the opposing magnetic poles overcome the reed stiffness causing them to flex toward each other and make contact. This operation can be repeated millions of times.
A biasing effect can be produced by placing a stationary magnet near a normally open reed switch to keep it closed. The approach of a second magnet with a reversed magnetic field will cancel the magnetic lines of force of the first magnet, and the switch will open.